Food waste could be used to pull lead, mercury from water

A foam filter made with used coffee grounds removes lead and mercury from contaminated water.

Here is a handy new use for those old coffee grounds: pulling lead out of drinking water.

A group of researchers has designed a foam made from coffee grounds and silicone that can remove lead and mercury from water. Both metals are contaminants considered toxic and harmful to human health.

Lead especially has been the subject of much attention in the wake of the contaminated water crisis in Flint, Michigan, as well as research suggesting many of the public water systems around the country may carry higher levels of lead than has been reported in the past.

The world produces around 6 million tons per year of spent coffee grounds, noted the new study, which conveniently have chemicals such as fatty acids, lignin, cellulose and polyphenols that absorb heavy metal ions.

This makes coffee, like some other plant products, a useful tool for filtering water. In fact, previous research has demonstrated the toxin-absorbing properties of coffee grounds and other food wastes such as eggshells and watermelon rinds.

However, there remains the matter of how one gets the grounds back out of the water once they have done their job.

Despina Fragouli and her colleagues at the University of Genoa and the Italian Institute of Technology developed a process that combines the grounds with silicone to form a porous foam (basically a sponge) that can be dropped into water. The small filter pulled out 99 percent of lead and mercury ions in about 4 teaspoons of still water after 30 hours.

In a separate test, the foam removed about 67 percent of lead in flowing water.

If the invention can be produced and distributed on a large scale, it may prove a cheap and effective way to reuse food waste, while helping to alleviate another serious public health concern.